unusual need for high pitch prop on Honda BF 2.3

I have a Hobie Tandem Island human powered hybrid pedal boat, I currently have the boat rigged with wing sails and a Honda bf2.3 motor for supplemental propulsion, primary propulsion is human pedal drive (twin mirage drive systems). The wing sails are so efficient, I only need to run the Honda at 1/4 throttle providing supplemental power (because I can't pedal fast enough by myself to provide enough power to make the wing sail work, thus the need for the supplemental motor). Since wing sails work on apparent wind (they create their own wind from your forward motion, you have to create the forward motion to get the chain reaction started). Wing sails increase in efficiency as speed goes up (the apparent wind passing over them, just like an airplane trying to take off, there is a minimum speed required for everything to start to work).
I run into the problem of over revving and blowing the engines up (already blew one up running at 1/4 throttle). I retro fitted a Tohatu 7" pitch prop onto the motor (easily done), but still have a severe speed limit and risk of blowing the motor at anything over 15 mph. The boat currently tops out at around 20mph.
My plan is to add a second BF2.3 engine, I already have the motor mounts made and basically ready to go. I can't go with anything heavier, and the reliability and durability of the Honda 2.3 for me is what I want on the boat offshore ( I sail mostly off shore South Florida gulf coast and Keys). When not needing the extra power I would just leave the second engine off the boat or tilted up as a safety backup. We are scuba divers and use the TI as our offshore dive boat (everything is all hardened on the boat for offshore use of course)
My question is how can I adapt a higher pitch prop onto the Honda 2.3. I have completed phase 1 and the boat has been operating for about a year now with the 7" pitch props and a single motor, the boat averages 7-10 mph in low winds (0 to 8mph winds regardless of actual wind direction, remember the wing creates it's own wind). I get over 100 miles per gallon. Basically I can go out all sailing day for between $.50 cents and a buck in fuel. Eighty percent of the year the natural winds here are below 6mph, so the boat is rigged specifically for this area, and extreme fuel economy.
Of course anyone can put a big ole motor on anything and go fast (I'm a former hydroplane racer and powerboater myself).
My phase II plans are to retrofit 10" pitch props onto twin BF-2.3 motors, and cruise at 15-20 mph at around 50-75 mpg (4x windspeed). The only 10" pitch props I can find are for 10 hp and up engines, I talked to Honda and they make absolutely nothing except the stock 4.5" pitch prop (no help there). My current plan is to find or build some sort of shaft adapter, then just buy a 9" dia x 10" pitch prop and turn the OD down to under 8" dia. Any ideas out there on how to get the higher pitch props onto the standard Honda pin shaft. I would prefer to buy off the shelf props if possible.

Phase III will be to add 12" or greater pitch props on the twin engines (once I have the hub adapter problem solved), and use my existing hydrofoils (already developed and built) and be able to cruise 30 mph at 50+ MPG fuel economy. ( 6 x windspeed). At higher speeds (over 30mph) obviously I won't be getting 50mpg.
Bob
My primary propulsion during phase 1 is my human powered pedal drives (2x windspeed currently), but they cannot be used at speeds over about 12 mph, so phases 2 and 3 will be with the motors, and wings (phase 3 with the hydrofoils)

 

I don't profess to understand exactly how this sail/motor set-up works, but if you can find a suitable prop with more pitch, a machine shop should be able to adapt it to fit fairly easily, and reduce the diameter. Go to an outboard wrecker, should be props there off old motors. It enters my mind that the problem you had with over-revving could turn into a "lugging" overloading problem that could blow it up just as quickly, but you know the characteristics of the boat better than me.

 

It occurs to me if the motor is revving it's little heart out with a small throttle opening, the boat is pulling the outboard along, why not just kill the engine and put it in neutral, or better still, tilt it ?

 

Mr Efficiency:
That is a very good idea, Once the chain reaction has started and the wing is working (perpetual motion), I'm just dragging that motor thru the water. With the motor locked on 1/4 throttle all day, the faster I go the higher the motor revs until it over revs and blows up (that's how I lost my first motor). I'm sure that lower unit has huge drag, here is a video of my boat just on a standard day, if you look at the back of the boat (at around 2.25 minutes into the video) you can see the huge drag the lower unit creates.

https://www.youtube.com/watch?v=bDGNxvCyVeI

I already have throttle and kill controls up in the cockpit, It wouldn't take much to add a couple 1/2 inch Bimba hydraulic cylinder some hydraulic line and a small rotary positive displacement rotary pump (like a powerwasher pump) up in the cockpit so I can tilt the motors up and down as needed while underway. I will add remote starter ropes so I can start the motors from the cockpit as needed because I sure I won't be able to tilt them up while running. Currently I just tilt the engine down and start it when I launch, then just leave it run all day (obviously just idling when I'm not going anywhere), when I get under way I lock the throttle to 1/4 throttle for the day. I'm out there every weekend all year round, since pedaling my boat 15 miles per week is my exercise program.
I only posted all this trying to explain kind of why I need the bigger props. And Since I don't know much about all the different kinds of props and adapters out there was hoping someone could provide information of or direct me to and off the shelf (easy) adaptor or something. It sound like there isn't much out there and I will basically need to just go buy the props and make an adapter myself just like I did to adapt the 7 inch pitch Tohatsu props to these motors. I blame Honda for not providing any alternate prop options for this motor ( a little mad about it), not everyone needs to push a 1500 lbs bass boat at 4 mph, my whole boat only weighs 200 lbs.
Thanks everyone

 

Fusioneng,
We used to tilt a Yamaha 9,9 remotely with a rope... a small dead eye on the cav plate gave 2:1 for the lift.

Jeff

 

Jeff:
Awesome idea and way easier to do, I'll do that
Bob

 

OK I have installed the second motor on my boat now here is a pic of the setup



Here is another pic with a closeup of the 8 inch dia 10" pitch props


Here is a short video of the boat under power at low throttle (under 1/4 throttle) with no sails up (the wing jib sail is not powered in this video)
https://www.youtube.com/watch?v=wmEbHyuOGCE

Keep in mind that the motors and props only provide a portion of the propulsion, as an example in the video the boat was traveling at 6.5mph at a little under 1/4 throttle, If I were to engage the wing and open the sails the boat would immediately accelerate to 10-12 mph at the same throttle setting. This throws a monkey wrench into all calculations regarding HP requirements.

One minor issue I ran into is the friction clutches on the motors start to slip and the engines once in a while increase in rpm (clutch slippage). My plan is to reduce the prop diameter to 7 inches and add a large radius on the leading edge.
keep in mind that the motors are not the primary propulsion, as the motors increase the boat speed (forward motion), the wing sail takes over and provides the majority of the hp requirements (about 20 hp at 15mph). Any suggestions on how to maintain the pitch (needed so as not to over rev the engines at speed), but reduce the rotational HP power requirement (ie... reduced prop diameter, radius's on edges, cupping, etc).
Any ideas out there.
Bob

 

Hi, I also live in sarasota, fl.

I was having problems with my honda 2hp cavatating on my outrigger canoe. Even at low throttle and much lower speeds than what you are talking about. The problem is that the motor is designed to have a transom in front of it rather than just hanging from an aka.

I fixed it by fabricating a simple fairing for the shaft housing. You can see a picture of it at the following links:

https://www.facebook.com/photo.php?fbid=10201139409955843&l=88cd84cc35
https://www.facebook.com/photo.php?fbid=10201139409755838&l=10f7301793

It might not solve your problem but maybe it would help?

Trent

 

Trent:
I actually came up with the same conclusion as you did. It appears that the motor is designed to mount behind the transom on a conventional boat, then if you mount it on the side of the boat (like both of us did), then you run into cavitation and drag problems. I ended up making a fairing that looks almost identical to yours, and all my problems went away.
Here is a pic of my final setup.


It's nice to know I'm on the right track.
Bob

 

Am I the only one confused with this system? First, I don't see anything that looks like a wing sail. Second I don't see much speed being developed. Looks like the boat would sail faster without any of the additional peddling and an outboard. Is there more than meets the eye in the video?

 

Tom:
In that video I didn't have any sails out at all, The wing jib is a wing sail that just follows the wind like a weather vane would, it free to rotate freely 360 degrees, and when in it's neutral symmetric shape creates no lift or drag. The jib basically an airplane wing about 6 inches thick but when in neutral has the same exact shape on both sides (not creating any lift or drag), just following the wind like a weathervane.
When you engage the wing jib by pulling it to one side or the other it changes shape into an asymmetric shape automatically (just like an airplane wing) thus creating lift (a vacuum in front of the boat), and also directing airflow across the main sail (making that much more efficient). Because there is no natural wind around here, I have to create my own wind with forward motion (the wing sail requires a minimum of 6mph of forward motion in order to begin amplifying the apparent wind. That's basically all the wing sail is just a giant amplifier just like a house air conditioner, basically taking existing energy, and amplifying to a greater power (more power out than in).

In the video above I was only showing only the motors running (no sails) because I was inquiring about prop designs.
In the area we live we very seldom get much wind 8-9 months out of the year, typical wind is 4-6 mph.
Here is a video of my TI with no motor running in the typical winds we have.
https://www.youtube.com/watch?v=zW62S1_RfYQ



I don't consider my boat as a sail boat, it's a human/hybrid powered pedal boat, basically specifically designed to operate in no to low wind conditions. With the twin Honda 2.3 engines running locked at 1/4 throttle the boat gets around 80 to 100 mpg fuel economy. I get 3 to 3 1/2 hrs run time averaging around 9-10 mph per tank of fuel (2 tanks 1 liter of fuel in each). This all in the same winds and the same general area you see in the above video. The boat creates it's own apparent wind via my forward motion. No different from how a piper cub operates, the propeller drives the plane forward, creating lift on the wings, if your engine quits while in the air you fall out of the sky. If my engines quit my boat stops ( I don't fall anywhere LOL). The engines only provide supplemental power (in order to create the forward motion that's starts the chain reaction). The boat has two mirage pedal drives mounted, I get the same effect with two strong peddler pedaling like mad (with no engines in the water (the engines only weigh 27 lbs ea so their weight means nothing as long as they are tilted up). Unfortunately after 1/4 to 1/2 mile or so we are so tired from pedaling like mad we can't continue, thus the reason for the engines (to maintain my forward motion), I can then pedal at a leisurely pace for up to ten hours, my typical outing every weekend is between 15 and 50 miles every weekend.
Here is another video with everything working and the boat is planing on top of the water ( the stock hull is a displacement hull with a max speed of 8 mph, so the hull was modified slightly to allow planing).
https://www.youtube.com/watch?v=a1OjgyqBsXk


The original post was regarding propeller design, I was trying to develop super high 14" pitch props so I could achieve 30mph plus speeds (on the foils) without exploding my motors (I have blown a couple up over revving them with this setup). I got all my questions answered and ended up with custom built 7" pitch props, however my speed limit with the 7" props in the water is currently around 15mph, anything over that and the motors over rev and explode. The boats top current speed is around 20 mph, but I must tilt the motors up, or switch to my 10" custom props, and must fly all 265 sq ft of sail in 20mph plus winds for all that to work, but that's getting a little to dangerous for this hull design so I typically just stay home if the winds are over 8mph. Of course if I have plenty of natural wind I just tilt the motors up and sail the old fashion way but that's only a couple weekends a year around here (SW Florida and the Keys), and not really what I built the boat for, it's designed specifically for very low winds and that's my only intent.
Thanks for the inquiry, but I'm all set.
Bob

 

Hmmmmmm...

 

Makes me want to look closer at a prop change on my Yamaha 2hp.

It will void the warranty.

But the prop is way too little and a spit of wind and I lose the bow.

Best of luck.

 

"(not creating any lift or drag)"...."basically taking existing energy, and amplifying to a greater power (more power out than in). "

Hmmmmmmmm....indeed!

 

Yes that’s basically it. Lets say for example the natural wind is 8mph and your pointed say 20 deg off the wind upwind. Now add your forward speed, (10mph) to the equation. This means you have 18mph of wind blowing on your face, (and over the sails). Once you get up to your initial speed with a power surge, ( from pedaling like mad, and a surge from the engine. The wing sail is engaged, (by changing it’s shape into an assymetric shape, and increasing the angle of attack on the wing). I can at that point pedal not as hard, and can decrease the throttle opening, (similar to a powerboat getting up on plane, ( your power requirements go down when on plane)). The wing basically redirects and focusses and organizes that 18mph wind into a concentrated stream of air, which it turn blows across and over the big main sail.
With the throttles locked, and pedaling at a constant pace, and the planing hull planing on top of the water. As the sails catch, the boat speeds up, and you can hear the rpm’s of the engines increase, ( the reason the engine rpm’s increase is because the propulsion load overhead requirements on the engines is taken over by wing/sail system. You can simulate this effect easily by taking any gas or electric motor, start it up and set to a fixed setting and measure the rpm of the prop while it is spinning in the air. Now with the same throttle setting plunge the prop into the water, (water is 1000 times more dense than air).
Basically what I’m doing with the human tripower hybrid system, is share the propulsion load overhead among all the systems, ( vs just the motors, or just the sails, or just the pedal drives). The reason for the twin engines is the two engines share the power overhead and help each other propel the boat forward, (obviouly the engines must be properly propped to take advantage of the effect).
I understand it’s a difficult concept to grasp. Why would anyone on earth with an outboard capable of providing 2.3hp hp at WOT, limit the engine output to 3/4hp, ( that’s just plain stupid, right). The Honda 2.3 at wot with it’s 1 liter fuel tank, on average gives you 1hr of runtime, (kind of an industry standard). With one engine running at WOT propped correctly propels a boat like the TI to 6mph, (lol very loud with much vibration), this is of course with no sails out in flat water. My setup averages 8-10mph cruise speed upwind in very low winds, I get 2-3hrs of runtime per tank of fuel, resulting in a fuel economy of around 80mpg, added benefit of the engines running at very low throttle is they are very quiet, with no vibration, (each engine is providing 3/4 hp, (1.5hp total). All of this is averaged out over 5 yrs of continous use, pretty much every weekend year round.
I have no idea why I continue trying to explain everything, (a total waste of everyones time), either you understand the concepts, or you don’t, (most don’t), so I’m wasting everyones time and energy trying to explain it all, It’s all easy to figure out yourselves if you think it all through.
The subject was solved back in 2013
FE